The HA-1, and later HA-1A, battery powered headphone amplifier was manufactured from 2002 through 2014. Approximately 900 units were built and sold. Serial numbers 200 and later had built-in AC power supply circuitry. The HA-1A is to the best of my knowledge the highest fidelity battery powered headphone amplifier that has ever been commercially manufactured.
I no longer manufacture or sell these HA-1A headphone amps, and have no current plan to do so; it was always a labor of love, and as life got busier and parts more expensive, it became impractical to continue. I do still support them under warranty; if you find one, buy it, no matter the condition, and I can restore it for you.
The AC adapter for the HA-1A is NOT STANDARD. Do not plug a regular 9VDC adapter into the HA-1A; it will not work and may damage the amplifier. You must use an adapter that produces 12V AC (not DC), with 500mA or more of current. Jameco.com part number 101258 is the adapter most HA-1As were shipped with, and is still available as of 2022.
The schematic diagram for the HA-1A is here, and the owner’s manual is here. Please feel free to contact Cafe Walter Audio on Facebook if you need additional information.